Gluconeogenesis

Question 1

What are the substrates for gluconeogenesis?

Answer 1

1. Lactate
2. Pyruvate
3. Glucogenic amino acids
4. Glycerol
5. Propionate

Question 2

Where the gluconeogenesis mainly take place? / Which is the primary site of production of glucose through gluconeogenesis in the body?

Answer 2

Liver

Question 3

When is glucose produced through gluconeogenesis in the kidney?

Answer 3

During starvation

Question 4

Why doesn’t gluconeogenesis take place in the skeletal muscles?

Answer 4

Because the skeletal muscles lack glucose-6 phosphatase.

Question 5

Why doesn’t gluconeogenesis take place in the smooth muscles, heart muscles or adipose tissue?

Answer 5

Because they lack fructose-1,6-bisphosphatase.

Question 6

What is the Cori cycle?

Answer 6

Cori cycle is the conversion of glucose to lactate in peripheral tissues (skeletal muscle and RBC), and the transfer of that lactate to liver to convert it into glucose.

Question 7

Does brain contribute to the cori cycle? Why?

Answer 7

Brain does not contribute to the Cori Cycle as it completely oxidises the glucose, and does not produce lactate.

Question 8

What is the significance of gluconeogenesis?

Answer 8

1. Supplies glucose to brain, nervous system, kidney, RBC, lens and testes.
2. It supplies glucose for energy after the glycogen supply is depleted after 12-18 hours of fasting.
3. It gets rid of metabolites in the blood such as lactate, pyruvate, propionate.
4. Supplies energy to skeletal muscles in anaerobic conditions.

Question 9

What regulates the entry of pyruvate to citric acid cycle or gluconeogenesis?

Answer 9

The concentration of Acetyl CoA.
Acetyle CoA inhibits Pyruvate dehydrogenase and stimulates pyruvate carboxylase.

Question 10

Which amino acids enter the TCA cycle by forming the TCA intermediates?

Answer 10

Pyruvate: Alanine, Glycine, Threonine, Serine, Cystein, Tryptophan
Fumerate: Tyrosine, Phenylalanine
Succinyl CoA: Isoleucine, Valine, Methionine
Alpha-ketoglutarate: Glutamine, Glutamate, Arginine, Histidine, Proline

Question 11

When are amino acids used for gluconeogenesis?

Answer 11

1. Starvation
2. Uncontrolled diabetes mellitus

Question 12

What is the Cahill cycle?

Answer 12

It is the formation of alanine in the muscle by its breakdown to give glutamate which combine with pyruvate through transamination. The alanine is transferred to liver which gives pyruvate again, that enters gluconeogenesis to give glucose, which is sent back to the muscle.

Question 13

How is glucose formed from glycerol?

Answer 13

Glycerol-> Glycerol 3 phosphate-> Dihydroxy Acetone 3 phosphate-> Glucose

Question 14

How is gluconeogenesis not the reversal of glycolysis?

Answer 14

Glycolysis has 3 irreversible steps:
1. Hexokinase
2. Phosphofructokinase
3. Pyruvate kinase

Question 15

Which enzymes help bypass the irreversible steps of glycolysis?

Answer 15

1. Hexokinase- Glucose 6 phosphatase
2. Phosphofructokinase- Fructose 1,6 bisphosphatase
3. Pyruvate kinase- Pyruvate carboxylase and phosphoenolpyruvate carboxykinase

Question 16

Which hormones regulate Gluconeogenesis?

Answer 16

1. Glucagon
2. Glucocorticoids
3. Insulin

Question 17

How do glucocorticoids stimulate gluconeogenesis?

Answer 17

Stimulates the synthesis of hepatic amino transferase.

Question 18

How does glucagon stimulate gluconeogenesis?

Answer 18

1. Stimulates the synthesis of G6P, G6 Phospatase and Fructose 1,6 bisphosphatase.
2. Represses the synthesis of HK, PFK and, PK

Question 19

What regulates fructose 1,6 bisphosphatase?

Answer 19

1. Stimulated by citrate
2. Inhibited by AMP